如何在latex中消除子图的标题中的括号？

\usepackage{caption}

\captionsetup[subfigure]{labelformat=empty}

\documentclass{article}
\usepackage{graphicx}
\usepackage{subcaption}
\usepackage{caption}

\begin{document}

\begin{figure}
  \centering
  \begin{subfigure}[b]{0.3\linewidth}
    \centering
    \includegraphics[width=\linewidth]{image1}
    \caption{子图1}
    \label{fig:subfig1}
  \end{subfigure}
  \begin{subfigure}[b]{0.3\linewidth}
    \centering
    \includegraphics[width=\linewidth]{image2}
    \caption{子图2}
    \label{fig:subfig2}
  \end{subfigure}
  \caption{整个图}
  \label{fig:whole}
\end{figure}

\captionsetup[subfigure]{labelformat=empty}

\begin{figure}
  \centering
  \begin{subfigure}[b]{0.3\linewidth}
    \centering
    \includegraphics[width=\linewidth]{image1}
    \caption{子图1}
    \label{fig:subfig1}
  \end{subfigure}
  \begin{subfigure}[b]{0.3\linewidth}
    \centering
    \includegraphics[width=\linewidth]{image2}
    \caption{子图2}
    \label{fig:subfig2}
  \end{subfigure}
  \caption{消除括号后的图}
  \label{fig:whole_without_brackets}
\end{figure}

\end{document}